1. Technical Field
The present invention relates to field of magnetoresistive sensors and may be utilized to improve spin-valve sensors.
2. Background Art
Spin valve sensors exploit changes in electrical resistance which occurs as a result of manipulating the relative orientation of the magnetization of ferromagnetic layers within a spin valve sensor. In conventional spin valve sensors, one ferromagnetic layer has its magnetization pinned while another, which has its magnetization set perpendicular to the pinned layer, is free to change its magnetic orientation in response to magnetized bits on an adjacent recording media. The magnetized bits on the recoding media, therefore, change the relative magnetization between the pinned layer and the free layer. An induced current through the spin valve is used to detect changes in the resistance of the spin valve that results from changes in the relative magnetization of the pinned and free layers.
The conventional spin valve utilizes an antiferromagnetic pinning layer adjacent the pinned layer to pin the direction of the magnetization of the pinned layer. The free layer, which may be made of several layers, is separated from the pinned layer by a thin nonmagnetic metallic layer.
Synthetic or improved spin valve sensors employ additional layers between the pinned layer and free layer/layers to create a laminate structure. Two additional layers are added: a second ferromagnetic layer, and a non-ferromagnetic material layer which separates the pinned layer and the second ferromagnetic layer and creates antiparallel coupling between the pinned layer and the second ferromagnetic layer. The first ferromagnetic pinned layer, therefore, causes the second ferromagnetic layer to be pinned antiparallel to the first pinned layer. Such a structure improves the longitudinal biasing of the free layer and therefore the spin valve's dynamic range, thereby allowing improved recording density.
As discussed above, the magnetic moment on the magnetic media changes the resistance across the spin valve which can be detected by passing a current through the spin valve. The giant magnetoresistance, one measure of the performance of a spin valve, is given by: EQU GMR=(R.dwnarw..Arrow-up bold.-R.Arrow-up bold..Arrow-up bold.)/R.Arrow-up bold..Arrow-up bold.
where,
GMR is the giant magnetoresistance ratio PA1 R.dwnarw..Arrow-up bold. is the resistance across the sensor when the magnetization of the layers are not aligned PA1 R.Arrow-up bold..Arrow-up bold. is the resistance across the sensor when the magnetization of the layers are aligned.
Spin valve layout and materials selection for the spin valve is critical to optimizing the GMR effect and sensor perfomance. It is an object of the present invention to provide an improved spin valve.